Changes in steady-state concentrations of messenger ribonucleic acids in luteal tissue during prostaglandin F2α induced luteolysis in mares

Transvaginal ultrasound-guided luteal biopsy was used to evaluate the effects of prostaglandin (PG)F2α on steady-state concentrations of mRNA for specific genes that may be involved in regression of the corpus luteum (CL). Eight days after ovulation (Hour 0), mares (n = 8/group) were randomized into three groups: control (no treatment or biopsy), saline + biopsy (saline treatment at Hour 0 and luteal biopsy at Hour 12), or PGF2α + biopsy (5 mg PGF2α at Hour 0 and luteal biopsy at Hour 12). The effects of biopsy on CL were compared between the controls (no biopsy) and saline + biopsy group. At Hour 24 (12 h after biopsy) there was a decrease in circulating progesterone in saline group to 56% of pre-biopsy values, indicating an effect of biopsy on luteal function. Mean plasma progesterone concentrations were lower (P < 0.001) at Hour 12 in the PG group compared to the other two groups. The relative concentrations of mRNA for different genes in luteal tissue at Hour 12 was quantified by real time PCR. Compared to saline-treated mares, treatment with PGF2α increased mRNA for cyclooxygenase-2 (Cox-2, 310%, P < 0.006), but decreased mRNA for LH receptor to 44% (P < 0.05), steroidogenic acute regulatory protein to 22% (P < 0.001), and aromatase to 43% (P < 0.1) of controls. There was no difference in mRNA levels for PGF2α receptor between PG and saline-treated groups. Results indicated that luteal biopsy alters subsequent luteal function. However, the biopsy approach was effective for collecting CL tissue for demonstrating dynamic changes in steady-state levels of mRNAs during PGF2α-induced luteolysis. Increased Cox-2 mRNA concentrations suggested that exogenous PGF2α induced the synthesis of intraluteal PGF2α. Thus, the findings are consistent with the concept that an intraluteal autocrine loop augments the luteolytic effect of uterine PGF2α in mares.